The scientific objective of this research project is to help us understand the processes and mechanisms involved in association formation. There are two main questions which this project is attempting to elucidate: 1) What is the role of the qualitative characteristics of a reinforcer in the formation of an association? and 2) How does the mutual or reciprocal generalization between stimuli affect stimulus control? Both of these questions are related in that they are of major importance in our attempt to understand how organisms learn. Moreover, these questions have important consequences regarding how one might efficiently maximize human learning and performance.